1. Field of the Invention
The present invention is in the field of biotechnology. More specifically, it relates to multifunctional proteins having two or more biological activities that are not found together in a single naturally occurring molecule. It further relates to the recombinant DNA that codes for M-CSF fusion proteins, the recombinant vectors that include the DNA, host organisms transformed with the recombinant vectors that produce the proteins, methods for producing the fusion proteins, pharmaceutical compositions containing the proteins and therapeutic methods employing the proteins.
2. Description of Related Disclosures
Recent technology has permitted the design of hybrid molecules which do not naturally occur. Fused selectable markers known as fusion flags to facilitate cloning, secretory leader peptide fusions to produce extracellular products and immunoconjugates are examples of such hybrid molecules. There have also been reports of attempts to produce hybrid proteins which possess potentially novel therapeutic properties by virtue of the combination of functions derived from each of the parent molecules. For example, hybrid interferons (IFNs) are disclosed in U.S. Pat. No. 4,758,428 and in European Patent Publication No. 0225579. Feng, G.-S. et al. (1988, Science 241:1501-1503) discloses a hybrid protein between IFN-.gamma. and TNF-.beta. which has increased antiproliferative activity in vitro compared with either IFN-.gamma. or TNF-.beta. alone. Japanese Patent Publication No. 61128889 discloses fusion proteins between IFN and urokinase. Hybrid plasminogen activators comprising, for example, fusions of urokinase and tissue plasminogen activator have also been reported. There are numerous disclosures of polypeptide-toxin hybrid proteins notwithstanding immunotoxins. For example, Kelley, V. E. et al. (1988, Proc. Natl. Acad. Sci. USA 85:3980-3984) report an IL-2/diphtheria toxin fusion protein which was found to be a potent immunosuppressive agent. U.S. Pat. No. 4,545,985 discloses IL-2/Pseudomonas exotoxin fusion proteins.
Another IL-2 fusion protein is disclosed in Australian Patent Abstract AU-A-66756/86 and European Patent Publication No. 0288809 (corresponding to PCT Patent Publication No. WO 87/02060) which report fusion proteins consisting of IL-2 and GM-CSF. The IL-2 sequence can be at either the N- or C-terminal end of the GM-CSF such that after acid cleavage of the fusion protein, GM-CSF having either N- or C-terminal sequence modifications can be generated.
In contrast, the present invention provides for the production of multifunctional proteins comprising M-CSF bioactivity produced by chemical or genetic fusion. Thus, the invention provides for the production of dimeric fusion proteins. It is surprising that these complex multifunctional homodimeric and heterodimeric proteins can be produced having two or more bioactivities since the refolding of M-CSF protein alone into its bioactive form is a complicated process. Furthermore, the multifunctional fusion proteins of the invention have increased therapeutic potential due to their multifunctional nature and their increased circulating half-life.